This invention relates to a liquid crystal display device and a process for making the same.
FIG. 9 shows an example of conventional liquid crystal display devices. This liquid crystal display device includes a first and a second substrates 41, 42. The first and the second substrates 41, 42 are disposed in parallel to each other.
The first substrate 41 includes an upper surface 41a provided with a polarizer plate 45 and a retardation plate 46. The polarizer plate 45 allows penetration of light rays that vibrate only in a specific direction. The polarizer plate 45 restricts entry of the light rays from the outside to the first substrate 41 or exit of the light rays from the first substrate 41. The retardation plate 46 is disposed between the first substrate 41 and the polarizer plate 45. The retardation plate 46 compensates for interference colors caused by birefringence at the liquid crystal. The retardation plate 46 enhances the viewing angle.
The first substrate 41 includes a lower surface 41b provided with a color filter layer 47. The color filter layer 47 may comprise a water absorptive resin, for example. The color filter layer 47 includes filter strips 47R, 47G, 47B. The filter strips 47R, 47G, 47B are colored red, green and blue, respectively. The filter strips 47R, 47G, 47B are arranged in parallel to each other in a widthwise direction.
The color filter layer 47 has a lower surface provided with a plurality of transparent electrodes 51 in the form of strips. The transparent electrodes 51 are arranged in corresponding relationship with filter strips 47R, 47G, 47B. The second substrate 42 has an upper surface 42a provided with a plurality of reflective electrodes 53 in the form of strips which extend perpendicularly to the transparent electrodes 51.
A liquid crystal layer 43 filled with liquid crystal is disposed between the first and the second substrates 41, 42. The liquid crystal layer 43 is surrounded by a seal member 55. Pixels are provided at the intersections between the transparent electrodes 51 and the reflective electrodes 53 in the liquid crystal layer 43. The pixels of the liquid crystal layer 43 are arranged in a matrix. A surface of the transparent electrodes 51 and a surface of the reflective electrodes 53 are covered, respectively, with an alignment films 54A, 54B. These alignment films 54A, 54B determine the twist of liquid crystal (liquid crystal molecules).
Light rays from the outside enter the above-described liquid crystal display device and travel through the polarizer plate 45, the retardation plate 46, the first substrate 41, the color filter layer 47, the transparent electrodes 51 and the liquid crystal layer 43. After travelling through the liquid crystal layer 43, the light rays are reflected upwardly by the reflective electrodes 53. The light rays reflected upwardly, then, travel back through the same path to be emitted to the front side of the liquid crystal display device.
The filter strips 47R, 47G, 47B of the color filter layer 47 provides corresponding colored regions 48R, 48G, 48B on the surface of the color filter layer 47, as shown in the FIG. 10. The colored regions 48R, 48G, 48B are strips provided in parallel to each other in a widthwise direction. Each of the filter strips 47R, 47G, 47B is provided when a color ink is supplied to the water absorptive resin of the color filter layer 47 by the ink-jet method, for example.
In the ink-jet method, an ink-jet printhead 57 is first arranged on a surface of the water absorptive resin applied on the surface 41b of the first substrate 41, as shown in the FIG. 11. Then, nozzles 57R, 57G, 57B of the ink-jet printhead 57 jet red, green or blue inks, respectively. In this way, the water absorptive resin is impregnated with the color ink. Each of generally circular dots 58 is provided by a color ink droplet on a surface of the color filter layer 47, as shown in the FIG. 12.
The ink-jet printhead 57, then, translates to the next row as viewed perpendicularly to the paper plain of the FIG. 12, and jets an ink. Thereby, a plurality of dots 58 are arranged partially overlapping with each other, providing the colored regions 48R, 48G, 48B. The diameter of the dots 58 may be approximately 90 xcexcm.
The size of the dots 58 may vary due to the state or the amount of the color ink jetted. When the diameter of the dots 58 varies by 10%, irregularities in the dot diameter will be in a range of approximately 81-99 xcexcm. As a result, when two dots between adjacent colored regions 48R, 48G, 48B are both diametrically smallest, the size of the clearance therebetween (indicated as A in the FIG. 12) is as large as about 9 xcexcm at the maximum.
When the dots have such diametrical irregularities in the colored regions 48R, 48G, 48B, clearances at boundaries of adjacent colored regions 48R, 48G, 48B may become relatively large. The boundaries between the adjacent colored regions 48R, 48G, 48B undulate due to the clearances. Therefore, in the liquid crystal display device incorporating the color filter layer 47 having such clearances and undulations, the filter strips 47R, 47G, 47B may not suitably mix different colors, thereby failing to provide proper color representation. The clearances and the undulations also deteriorate the image quality.
In order to eliminate the clearances and the undulations described above, a black matrix that intercepts light may be provided at the boundaries of the filter strips 47R, 47G, 47B. However, formation of a black matrix may require photolithography, the manufacturing process may become complex, consequently resulting in an increase of production time and cost. Other methods may include providing a barrier wall or water repellent treatment at the boundaries of the filter strips 47R, 47G, 47B on a surface of the water absorptive resin 56 for preventing color ink deposition. However, these methods also require time and increase the cost.
It is therefore an object of the present invention to provide a liquid crystal display device which is capable of eliminating or at least reducing the problems described above.
In accordance with a first aspect of the present invention, there is provided a liquid crystal display device comprising: a first and a second substrates disposed in parallel to each other; a liquid crystal layer disposed between the two substrates and filled with liquid crystal; and a color filter layer disposed on a surface of the first substrate facing the second substrate;
wherein a surface of the color filter layer is provided with plural filter strips each retaining a respective color ink; and
wherein each of the filter strips includes plural columns of and plural rows of generally circular dots arranged in a strip or rectangle, each of the dots being provided by a color ink droplet.
Preferably, the color filter layer may comprise a water absorptive resin.
Preferably, each of the filter strips may be provided by impregnating the water absorptive resin with a respective color ink.
Preferably, each of the dots may be 20-40 xcexcm in diameter.
Preferably, adjacent ones of the dots may partially overlap each other.
Preferably, the color inks may include red, green and blue inks.
Preferably, the liquid crystal in the liquid crystal layer may be controlled by voltage application in a normally black mode.
In accordance with a second aspect of the present invention, there is provided a process for making a liquid crystal display device which comprises: a first and a second substrates disposed in parallel to each other; a liquid crystal layer disposed between the two substrates and filled with liquid crystal; and a color filter layer disposed on a surface of the first substrate facing the second substrate; the process comprising the steps of:
applying a water absorptive resin onto the surface of the first substrate facing the second substrate to form an ink retaining layer that serves as the color filter layer; and
jetting different color inks onto the ink retaining layer to form filter strips at each of which the water absorption resin is impregnated with a respective color ink;
wherein the step of providing the filter strips is performed in a manner such that each of the filter strips includes plural columns of and plural rows of generally circular dots arranged in a strip or rectangle, each of the dots being provided by a color ink droplet.
Preferably, the step of forming the filter strips may include jetting different color inks onto the ink retaining layer by an ink-jet method.
Preferably, the water absorptive resin may comprise polyvinyl alcohol.
The other features and advantages of the present invention will be clarified in the detailed description given below with reference to the accompanying drawings.